Corrugated board constructions

ABSTRACT

CORRUGATED BOARD CONSTRUCTIONS HAVING INCREASED WET STRENGTH ARE MADE BY LAMINATING AT LEAST TWO SHEETS OF MATERIAL SUITABLE FOR CORRUGATING, WITH AN ASPHALT MATERIAL HAVING A SOFTENING POINT OF FROM 150 TO 240*F., PENETRATION VALUES AT 32*F., 200 GRAMS, 60 SECONDS OF 4 TO 11 MM./10, AT 77*F., 100 GRAMS, 5 SECONDS OF 6 TO 18 MM./10, AT 115*FL, 90 GRAMS, 5 SECONDS OF 20 TO 35 MM./10 AND VISCOSITY (SAYBOLT FUROL) AT 350*F. OF 150 TO 1000 SECONDS, CORRUGATING THE RESULTING LAMINATE AND ADHERING AT LEAST ONE SUBSTANTIALLY FLAT LINER BROAD TO THE RESULTING CORRUGATIONS.

March 14, 1972 S. H. ALEXANDER CORRUGATED BOARD CONSTRUCTIONS Filed July 13. 1970 ATTORNEY United States Patent O 3,649,432 CORRUGATED BOARD CONSTRUCTIONS Stephen H. Alexander, St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo. Continuation-impart of application Ser. No. 430,821, Feb. 8, 1965. This application July 13, 1970, Ser.

Int. Cl. B32b /28 US. Cl. 161-137 7 Claims ABSTRACT OF THE DISCLOSURE Corrugated board constructions having increased wet strength are made by laminating at least two sheets of material, suitable for corrugating, with an asphalt material having a softening point of from 150 to 240 F., penetration values at 32 F., 200 grams, 60 seconds of 4 to 11 mm./10, at 77 F., 100 grams, 5 seconds of 6 to 18 mm./l0, at 115 F., 50 grams, 5 seconds of 20 to 35 mm./ 10 and a viscosity (Saybolt Furol) at 350 F. of 150 to 1000 seconds, corrugating the resulting laminate and adhering at least one substantially flat liner board to the resulting corrugations.

This application is a continuation-in-part of my application Ser. No. 430,821 filed Feb. 8, 1965, now abandoned.

The present invention relates to corrugated board constructions. More particularly, the present invention relates to corrugated board constructions and a method for their preparation, which constructions possess substantially improved wet-strength properties.

BACKGROUND OF THE INVENTION Generally, corrugated boards consist of a corrugated sheet, usually a corrugated paper sheet, and at least one substantially fiat lining sheet, also usually paper, joined to the crests of the corrugations on at least one side of the corrugated sheet. More often a second substantially fiat lining sheet is joined to the crests of the corrugations on the side of the corrugated sheet opposite the first lining sheet. The corrugated sheet is joined to the lining sheet or sheets by means of an adhesive material such as a starch adhesive, applied to the crest of the corrugations of the corrugated sheet. Corrugated board is used, principally, in the construction of containers and spacing media for containers. Such containers and spacing media are used for the packaging of a vast multitude of materials.

In many instances, corrugated board containers are used to package materials which are wet or which must be packed in ice, Also, such containers often must be stored in damp areas or in other wet environments. In such utilities, it is necessary that the corrugated board be of such composition that it will retain considerable strength within such wet environments. The measure of the maintenance of strength within a wet environment is usually referred to as Wet-strength.

Ordinary corrugated paperboard does not process particularly good wet-strength. Water readily penetrates and softens either or both the lining sheets and, upon contacting the corrugated paper sheet, will soften it, also. To improve the wet-strength of corrugated paperboard it has been proposed to waterproof the lining sheets by applying various waterproofing agents such as waxes, polyvinylacetate-wax blends and the like to the outer surfaces of those lining sheets. However, it is very dimcult to prevent some moisture from reaching the interior of the corrugated paperboard when containers of such material are in contact with a very Wet environment.

3,649,432 Patented Mar. 14, 1972 ice SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and improved corrugated board construction. An additional object of the present invention is to provide a method for preparing a new and improved corrugated board construction. Another object of the present invention is to provide a method for imparting improved wet-strength to corrugated pape-rboards. Still another object of the present invention is to provide a novel corrugated paperboard possessing improved wet-strength. It is also an object of the present invention to provide a method for the preparation of a corrugated paperboard possessing improved wet-strength. Additional objects will become apparent from the following description of the invention herein disclosed.

The invention which fulfills these and other objects is a corrugated board construction comprising a corrugated sheet having attached to the crests of the corrugations thereof at least one substantially fiat outer lining sheet, said corrugated sheet comprising at least two sheets laminated with asphalt, said asphalt having a softening point of 150 to 240 F., a penetration at 32 F., 200 grams, 60 sec. of 4 to 11 mm./10, a penetration at 77 F., grams, 5 sec. of 6 to 18 mm./l0, a penetration at F., 50 grams, 5 sec. of 20 to 35 mm./l0, a viscosity S. Furol at 350 F, of to 1000 sec. and a carbon tetrachloride solubility of 99.5 weight percent.

DESCRIPTION OF PREFERRED EMBODIMENTS In a preferred embodiment, the corrugated board composition of the present invention is one in which the substantially fiat outer lining sheets and the corrugated sheets are a paper, paperboard, or cardboard.

The corrugated board constructions described above are normally prepared by laminating two or more sheets of material suitable for corrugating with the above described asphalt, corrugating the resulting laminate and adhering at least one substantially flat outer lining sheet to the corrugations of the corrugated laminate. It is, of course, within the scope of the present invention to use other conventional means for producing corrugated board constructions employing the above described asphalt.

Corrugated boards of the construction disclosed and described herein possess substantially greater wet strength than ordinary corrugated boards. Further, the corrugated boards of the present invention possess substantially improved dry strength as compared to conventional corrugated boards.

In order to further describe the present invention, reference is made to the accompanying drawing which represents a cross-sectional diagrammatic view of a corrugated board prepared in accordance with the present invention. In reference to the drawing, two flat lining sheets 10, usually paper, are placed one on either side of a corrugated laminate sheet 11 which consists essentially of two corrugated sheets 12 bonded together by means of an asphalt lamina 13. Lining sheets 10 are united to the corrugated sheet by means of an adhesive 14 at the crests 15 of the corrugations.

To demonstrate the present invention as well as to further describe its practice, the following examples are presented. These examples are in no manner to be construed as limiting the present invention.

EXAMPLE I A corrugated paperboard was prepared by laminating two sheets of paper with an asphalt having the following properties:

Softening point, F. (R & B) 190 Penetration at:

77 F., 100 grams, sec 9 32 F., 200 grams, 60 sec. 6 115 F., 50 grams, 5 sec. Viscosity S. Furol at 350 F. sec 250 The asphalt laminant having the above properties was prepared by air-blowing to the indicated 190 F. softening point a propane extracted asphalt having a penetration at 77 F., 100 grams, 5 seconds of 85 to 100 mm./ 10 which had been derived from a steam and vacuum distilled light Arkansas crude.

The asphalt laminant was applied at a temperature of 355 F. in an amount of lbs. of asphalt per 1000 square feet of surface of one sheet of paper to which another sheet was then laminated. The resulting asphalt laminated paper was then corrugated and the resulting corrugated laminate united with two flat sheets of linerboard, one on either side to form a corrugated paperboard. To unite these two sheets of linerboard with the corrugated sheets, a starch adhesive was applied to the crests of the corrugated sheet and the two flat linerboard sheets placed in contact therewith.

To illustrate the advantages of the compositions of the present invention, a portion of the sheet of corrugated paperboard prepared above was compared with a similar corrugated paperboard of the same construction with the exception that a different asphalt was used in its preparation. This alphalt was one having the following properties:

Softening point, F. (R & B) 185 Penetration at:

77 F., 100 grams, 5 sec 21 32 F., 200 grams, 60 sec l3 115 F., grams, 5 sec. 40 Viscosity, S. Furol at 350 F., sec. 205

The asphalt laminant having the above properties was prepared by air-blowing to a softening point of 185 F. an asphalt having a penetration at 77 F., 100 grams, 5 seconds of 200 to 250 mm./ 10 and derived from a Smackover crude which had been steam and vacuum distilled. Comparison was carried out by immersing each of the two corrugated paperboards in water for a given period of time and then determining the bursting strength by the method of T 403ts-63 of the Technical Association of the Pulp and Paper Industry. The following table presents the bursting strength in p.s.i. which is a measure of the wet-strength of each of these corrugated boards after the varying intervals of immersion time.

Immersion time of board Construction 1 hr. 2 hrs. 3 hrs. 4 hrs.

Corrugatedboard of present invention..- 117 98 89 86 Corrugated board using asphalt not within present invention 73 70 7t) 70 tion may be derived from a variety of sources but have in common the following properties:

Softening point, F. 150-240 Penetration. at:

77 F., grams, 5 sec. 6-18 F., 50 grams, 5 sec 20-35 32 F., 200 grams, 60 sec 4-11 Viscosity, S. Furol at 350 F., sec. -1000 Solubility in CCl wt. percent 980-100 A particularly useful asphalt for the compositions of the present invention is one having the following properties:

Softening point, F -220 Penetration, at:

77 F., 100 grams, 5 sec. 8-16 115 F., 50 grams, 5 sec 24-33 32 F., 200 grams, 60 sec. 5-10 Viscosity, S. Furol at 350 F., sec. -500 Solubility in C'Cl wt. percent 990-100 The asphalts useful in the corrugated board construction of the present invention are obtained by a variety of commonly used refining or treating processes. For example, an asphalt with the necessary combination of properties set forth above can be prepared by solvent extracting and then air-blowing a much softer starting asphalt as set out in Example I above. An asphalt likewise having this combination of properties can also be prepared by airblowing of a softer asphalt to the desired softening point range. Likewise, suitable asphalts with the necessary combination of properties can be produced by processes such as distillation and steam and/or vacuum reduction of certain crudes, also combined, if desired, with airblowing. Such useful asphalts may be obtained from a variety of crude oils such as California crudes, South Arkansas crudes. East Texas crudes, Mexican petroleum asphalts and the like. A particularly useful source of the asphalts useful in the present invention is an air-blown asphalt obtained from a South Arkansas crude.

Asphalts having the combination of properties and useful in the corrugated board constructions of the present invention have been known and available commercially for certain purposes, but have not been previously employed as laminants in corrugated board constructions. For example, an asphalt having the necessary combination of properties for use in the present invention, but disclosed for use in coating a single paper ply is described in the text Bituminous Materials: Asphalts, Tars, and Pitches, vol. H Asphalts edited by Arnold I. Hoiberg published by Interscience Publishers (1965) in Table 20-16 at page 651.

The amount of asphalt used in preparing the corrugated paperboard constructions of the present invention will vary to some extent with the proposed use of the paperboard and with the materials used for forming the corrugated sheets and outer lining sheets. For most intended uses, however, the amount of asphalt used will be within the range of 0.005 to 0.06 lb. of asphalt per square foot of surface of the sheet to which it is applied. Usually, as strength requirements increase, the amount of asphalt used will also increase, however, seldom if ever will it exceed the above defined limit.

Constructions according to the present invention may contain as outer lining sheets and corrugated sheets any of the materials conventionally used for such purpose. Included within this category are outer lining sheets and corrugated sheets of paper, paperboards, fabrics, cardboards, plastics, and the like. The most useful corrugated board constructions of the present invention are those containing paper, paperboard or cardboard as the outer lining sheets and the corrugated sheets.

The corrugations of the laminated corrugated sheets of the present constructions may be varied widely depending upon the utility to which the corrugated board compositions are to be put. Usually, however, conventional designs are used varying from 36 flutes per lineal foot, inch high, to 50 flutes per lineal foot, to /8 inch high. The number and height of the flutes of the corrugated medium of the present composition, while important for a particular use, are not critical to the present invention since the improvements obtained by the present compositions are based upon improvements over corrugated boards of substantially the same general construction with the exception of the construction of the particular laminated corrugated sheets of the present invention.

The number of sheets or laminae in the corrugated laminated sheets of the present construction is at least two. However, more than two sheets may be laminated to form the corrugated sheet. Preferably, however, two sheets are used.

The adhesives useful for adhering the outer lining sheet or sheets include all of those conventionally used as well as other materials suitable for such purpose. Such adhesives include, but are not limited to starch, casein, rubber latex, phenolic resins, polyester resins, and the like.

In addition to the above described components of the corrugated board constructions disclosed and described herein, it is often desired to add a waterproofing agent to one or both of the outer lining sheets. Such waterproofing agents may be any of those known to the art for such utility. These include various petroleum derived impregnants such as asphalts, petroleum waxes, etc., various natural waxes, polymeric films such as polyvinyl chloride, polyvinyl acetate, polyvinyl chloride-polyvinylacetate copolymers, polyethylene, etc. and blends of the above, both with one another and with other suitable materials. Often the choice of waterproofing agent depends almost entirely on the subsequent use of the corrugated board. Waterproofing agents such as petroleum derived asphalts cause the impregnated surface to be black which for many utilities is undesirable.

The corrugated board compositions of the present invention find particular use in the preparation of containers such as boxes which are used in packing materials which must be maintained in a wet environment, eg ice, or boxes must be stored in Wet surroundings. For example, the corrugated board constructions of the present invention are particularly useful for the preparation of boxes for shipping meats which must be kept iced with wet ice. Also, when corrugated boxes are to be shipped or stored in refrigerated freight cars and the like, the corrugated board constructions of the present invention are particularly useful.

The method whereby the laminated corrugated sheet of the present corrugated board constructions is laminated most often comprises coating a sheet of material suitable for corrugating with the asphalt bonding agent disclosed and described herein, adhering a second sheet of such material to the asphalt surface opposite the first sheet and thereafter corrugating the resulting laminate. The asphalt is usually applied to the first sheet of material suitable for corrugating at an elevated temperature sufficiently high to reduce the viscosity of the asphalt enough to allow it to be readily coated onto the surface of the sheet and to adhere to the sheet. Application of the asphalt to the surface of the first sheet may be by any conventional method including, but not limited to brushing, rolling, spreading, spraying and the like. In order to facilitate coating the surface of the first sheet with the asphalt, particularly by such methods as spraying, it may be desirable to mix a viscosity reducing agent such as a light naphtha, heptane, hexane, or the like with the asphalt. However, the addition of a viscosity reducing agent is seldom practical because of the difficulties arising out of removing the agent from the asphalt and the lack of desirability of having such in the resulting laminated corrugating sheet. The second sheet of paper suitable for corrugating is joined with the asphalt surface opposite the first sheet of paper, generally while the asphalt is still at elevated temperatures. Usually to insure lamination of the two sheets by the asphalt, pressure is applied to one or both surfaces of the laminate while the asphalt is still at a slightly elevated temperature. This is usually done by passing the laminated sheet between two rollers The resulting laminated sheet is then corrugated by any conventional means. The only restriction on corrugation is that the laminated sheet be corrugated with the asphalt in the laminated sheet sufficiently soft to be flexible enough to allow corrugating without cracking or breaking of the asphalt.

What is claimed is:

1. A corrugated board construction comprised of a corrugated sheet having attached to the crests of the corrugation thereof at least one substantially flat lining sheet, said corrugated sheet comprising a laminate of at least two corrugated sheets laminated together with asphalt, said asphalt having a softening point of 150 to 240 F., a penetration at 32 F., 200 grams, 60 sec. of 4 to 11 1nm./l0, a penetration at 77 P., grams, 5 sec. of 6 to 18 mm./10, a penetration at F., 50 grams, 5 sec. of 20 to 35 mm./ 10, a viscosity (Saybolt Furol) at 350 F. of to 1000 see. and a CCL, solubility of 98.0 to 100% by weight.

2. The construction of claim 1 wherein said corrugated sheet has attached to the corrugations thereof, two substantially flat outer lining sheets, one on each side of said corrugated sheet.

3. The construction of claim 1 wherein said corrugated sheets and said substantially fiat outer lining sheet are a material selected from the group consisting of paper, paperboard and cardboard.

4-. A method for the preparation of corrugated board constructions which comprises laminating at least two sheets of a material suitable for corrugating, with an asphalt having a softening point of 150 to 240 F., a penetration at 32 F., 200 grams, 60 sec. of 4 to 11 mm./ 10, a penetration at 77 F., 100 grams, 5 sec. of 6 to 18 mm./10, a penetration at 115 F., 50 grams, 5 sec. of 20 to 35 mm./ 10, a viscosity (Saybolt Furol) at 350 F of 150 to 1000 sec. and a CCl solubility of 98.0 to 100% by weight, corrugating the resulting laminate, adhering at least one substantially flat linerboard to the corrugations of the corrugated laminate.

5. The method of claim 4 wherein a substantially flat linerboard is adhered to each side of the corrugated laminate.

6. The method of claim 4 wherein the material suitable for corrugating and the substantially flat linerboard are a material selected from the group consisting of paper and paperboard.

7. The method of claim 4 wherein the amount of asphalt used in laminating said materials suitable for corrugation is within the range of 0.005 to 0.06 lb. of

asphalt per square foot of surface of one of the sheets laminated.

References Cited UNITED STATES PATENTS 1,119,146 12/1914 Ferres 16l137 X 1,605,953 l1/1926 Howard l6l-l37 X 3,329,636 7/1967 Henschel 161-238 X WILLIAM A. POWELL, Primary Examiner US. Cl. X.R. 

